1. Field of the Invention
A device for the angular adjustment of a camshaft(s) of a combustion engine according at least to speed and load conditions and to the angular position of the camshaft with respect to the engine crankshaft. In this way, camshaft timing may be advanced or retarded dynamically thus altering the torque characteristics of the engine on a continuous basis. Furthermore, if two separate camshafts--one intake, one exhaust--are independently alterable, then valve overlap timing may also be dynamically controlled.
2. Description of the Prior Art
In general, the camshafts of a combustion engine are coupled to the crankshaft by a toothed belt and therefore they are driven synchronously with the crankshaft. As a result of this the opening phase of the intake and exhaust valves as well as the overlap angle are constant. This is especially true in the case of a single camshaft containing both intake and exhaust lobes. So, these values can only be adapted to an average value. As is known, the optimum state for the overlap angle changes depending on speed, on load, and on temperature in the combustion chamber: the greater the speed, the greater the overlap required to maximize engine torque.
In the patent application DE-OS No. 29 09 803 there has been described a device of the type mentioned at the beginning. A helical bushing within a helical gear is controlled by centrifugal force whereby the angular position of the camshaft with respect to the crankshaft is adjusted.
U.S. Pat. No. 4,305,352 Oshima, et al. shows a device for camshaft control with an epicyclic gear to adjust the camshaft. A control device not described in detail provides the correcting variables.
A device for camshaft control according to DE-OS No. 25 25 746 also comprises a planet gear for adjusting the camshaft, the control input of the gear being connected with a stepping motor. The instantaneous angular position is continuously compared with the set value. The stepping motor is controlled according to the deviation. It is not described in this application in which way the set values are deduced.
This invention differs from the prior art in a way not obvious in that the digital values of speed and load are evaluated in a digital process, stored values of the angular adjustment being pre-assigned to the digital input data.